The defense team for embattled New York lawyer Steven Donziger wants the judge presiding over his civil racketeering trial to strike testimony from a key witness for the opponent, Chevron

The reason?

According to a motion filed Wednesday in Manhattan federal court, the “outrageous nature and extent of Chevron’s payments” to the witness—an Ecuadorean former judge named Alberto Guerra Bastidas. Mr. Guerra says he ghostwrote rulings for another judge in an environmental case that ultimately resulted in a $19 billion verdict against the oil giant and in favor of Mr. Donziger’s clients.

Chevron says the Ecuadorean judgment was fraudulently obtained and that the company is being extorted by Mr. Donziger and others representing Ecuadorean villagers who sued the company over alleged pollution from oil exploration in the Amazon Basin. Mr. Donziger denies those claims.

Chevron’s case will likely turn in part on the testimony of Mr. Guerra, who outlined a rather eye-popping tale of bribes, clandestine meetings and judicial misconduct during his two-and-a-half days in court last week.

Randy Mastro, a partner with Gibson Dunn & Crutcher LLP representing Chevron, called the defense’s Wednesday motion “a PR stunt,” adding: “We believe we are proving beyond any doubt our racketeering and fraud claims, and we look forward to concluding the trial and seeing that justice is served.”

Testifying in Spanish through an interpreter last week, Mr. Guerra told U.S. District Judge Lewis A. Kaplan that he routinely drafted rulings for Judge Nicolas Zambrano, who presided over the case on two separate occasions. (Mr. Zambrano has denied the claims, and is expected to testify for the defense later on in the trial).

Mr. Guerra also said he met with Mr. Donziger and an Ecuadorean lawyer for the plaintiffs, Pablo Fajardo, at a Quito restaurant called Honey Honey to discuss swaying the case in their favor. Later, Mr. Guerra said, Mr. Fajardo provided him with a laptop, which he used to review the final judgment for the environmental case—a document he claimed had been written by the Ecuadorean plaintiffs’ team. “I found out through Mr. Zambrano, because he told me so himself,” Mr. Guerra said.

During cross-examination Mr. Donziger’s lawyer, Zoe Littlepage, pointed out what she said were inconsistencies in various accounts Mr. Guerra has given of the alleged fraud over the past two and a half years. She drew attention to the fact that physical evidence submitted in the case, such as bank deposit slips showing payments to Mr. Guerra and day-planner entries documenting his contacts with Mr. Zambrano, largely skipped over the period leading up to the Feb. 14, 2011 verdict.

Money, and Mr. Guerra’s apparent desire for more of it, also occupied much of this cross-examination by Ms. Littlepage, who cited some rather embarrassing statements he made to Chevron representatives when discussing payment for evidence of the alleged fraud.

When Mr. Guerra learned during one encounter with Chevron’s representatives that they had $20,000 in cash on them, “did you respond, ‘Can you add a few zeros?’” asked Ms. Littlepage. He did, he conceded, but said he was joking.

And did he say “Money talks but gold screams,” she asked. He didn’t recognize that particular adage, Mr. Guerra said, “but in one way or another I did express that feeling.”

Mr. Donziger’s defense team also emphasized the thousands of dollars and other benefits Chevron has given Mr. Guerra since he came forward. Among them:

$48,000 for the physical evidence he provided, including a laptop computer and electronic records, and to compensate Mr. Guerra for gathering other evidence including bank and travel records.

$2,000 per month for rent, plus $10,000 per month to cover living expenses for him and his family after Chevron paid to relocate them to the U.S., citing security concerns.

Health insurance and legal representation, including immigration lawyers, for Mr. Guerra and his family.

Chevron has previously disclosed the payments, and says that Mr. Guerra is not being paid to testify. The company says the payments are reasonable given the expenses he incurred to provide the evidence, and the potential danger Mr. Guerra would have faced had he remained in Ecuador.